Winglets are used to reduce induced drag on aircraft wings. According to the “Trefftz plane theory” the induced drag depends only on the “spanload” and the trailing edge trace of the “lifting system” (i.e., the wing plus tip device), as viewed directly from the front or rear of the wing. The spanload is the distribution of aerodynamic load perpendicular to the trailing edge trace of the wing. Adding a winglet to a wing changes both the trailing edge trace (i.e., the “Trefftz-plane geometry”) and the spanload. Adding such a device also changes the induced drag on the wing.
The winglet may be added to a wing by removing a tip of the wing and fastening the winglet to the remaining outboard portion. However, adding the winglet can create interference effects between the wing and the winglet. The interference effects can increase drag and/or reduce lift, which adversely affect aircraft performance.
It is desirable to reduce or eliminate the interference effects.